sun gear; sun wheel
Technical term in mechanical engineering; the central gear in a planetary gear train.
In a planetary gear mechanism, the sun gear is placed at the center.
Planet gear; meshes with the sun gear and ring gear in a planetary gear set.
Ring gear (internal gear); the outer gear with teeth on the inside, meshing with planet gears.
Compound of 太陽 (taiyō, 'sun') + 歯車 (haguruma, 'gear'), calque of English 'sun gear'.